JP2005195499A - Sdi measuring method, sdi measuring instrument, and water production method using reverse osmosis membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an SDI measuring method for calculating highly accurate SDI values at all times to estimate contamination risk of a separation membrane in advance in order to stably operate a membrane process thereafter, and to provide an SDI measuring instrument; to provide a water production method using a reverse osmosis membrane including a process for measuring the SDI value by using the same method. <P>SOLUTION: This SDI measuring method is characterized in that the SDI values of a separation membrane supplying liquid are measured by using a membrane filter with a contact angle θ equal to or less than 70°. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an SDI measurement method used for a water pollution index of separation membrane feedwater in a membrane process, and more particularly to an SDI measurement method that can always calculate a highly accurate SDI value. Further, the present invention relates to an SDI measuring device used in the method and a water production method using a reverse osmosis membrane including a step of measuring an SDI value by the method.

  Raw water such as seawater and sewage contains various suspended substances, colloidal organic and inorganic substances, contaminants such as viruses and bacteria. Such contaminants contaminate the separation membrane and cause a decrease in performance.

  Conventionally, in seawater desalination treatment and sewage regeneration treatment using a separation membrane such as a reverse osmosis membrane, in order to prevent contamination of the separation membrane, processes such as coagulation sedimentation treatment, pressurized flotation treatment, and sand filtration treatment are performed in advance. In combination, a pretreatment process has been performed to remove particulate components such as microorganisms, colloids, and silt in raw water. In recent years, techniques for pretreatment of raw water by membrane separation such as microfiltration membrane (MF) and ultrafiltration membrane (UF) have been developed. And, as a method of measuring the degree of contamination due to trace suspended substances in water after removing fine particle components, a method using a membrane filter with a uniform fine pore size and the clogging rate as the contamination index is adopted. Has been. In particular, it has been confirmed that it is very effective for prevention of membrane contamination as a monitoring index of water supplied to a reverse osmosis membrane seawater desalination apparatus. Currently, ASTM (Standard Test) is used as a water pollution index of separation membrane supply water in a membrane process. The SDI (Silt Density Index) measurement method prescribed | regulated by Method for Silt Density Index of Water D4189-95 (2002) is generally used.

  The SDI value (contamination index) calculated by the SDI measurement method is calculated by the following calculation formula.

SDI ₁₅ = (1-T ₀ / T ₁₅ ) × 100/15
T ₀ : Time (seconds) required to filter a sample at a pressure of 206 kPa through a membrane filter having a pore diameter of 0.45 μm and a diameter of 47 mm and filter an initial sample of 500 ml
T ₁₅ : Continued for 15 minutes after the start of filtration, and then time (seconds) required to filter 500 ml of the sample
The value of SDI _{15 is} a value from 0 to 6.66, and the greater the value, the greater the degree of contamination. Generally, the SDI value of water supplied to the reverse osmosis membrane after pretreatment of raw water such as seawater and sewage is 4 or less.

  For the purpose of providing a fresh water generation method using reverse osmosis separation that improves the recovery rate of fresh water from seawater to reduce freshwater production costs and further reduces equipment costs, A fresh water generation method of controlling to 1 or less is disclosed (Patent Document 1). And as a method of controlling the SDI value of the seawater to be supplied to 1 or less, a method of membrane-treating raw seawater with a membrane separator, and a method of performing membrane treatment after pretreatment of the raw seawater in advance are described. .

However, in recent years, when the SDI value of pre-treated membrane filtrate is measured using the above SDI measurement method, the SDI value does not necessarily indicate an accurate value, and it is clear that there is a problem in the accuracy of the contamination index. Became. In particular, when microbubbles were present, it became clear that the values were significantly different from normal SDI values. For example, an ultrafiltration membrane having a pore size smaller than a membrane filter having a pore size of 0.45 μm used for SDI measurement (nominal fractional molecular weight: 20000 Daltons, nominal pore size: 0.007 μm, or nominal fractional molecular weight: 500,000 Daltons, nominal pore size : It is often recognized that the SDI value of membrane filtration water after pretreatment of seawater etc. using a microfiltration membrane with a pore size of about 0.1 μm shows an abnormally large value exceeding 3. It was. Therefore, in order to predict the contamination risk of the separation membrane in advance and to stably operate the membrane process, it has been desired to develop an SDI measurement method that can always calculate a highly accurate SDI value.
JP 2001-252661 A

  The present invention solves the above-mentioned problem, and predicts the contamination risk of the separation membrane in advance, and can stably calculate a highly accurate SDI value in order to stably operate the subsequent membrane process. It is to provide a method. Another object of the present invention is to provide an SDI measuring apparatus used in the above method and a water production method using a reverse osmosis membrane including a step of measuring an SDI value by the above method.

  The present inventors have found that the above-mentioned problems can be solved by the following method as a result of intensive studies in view of the above-described situation.

  That is, the present invention relates to an SDI measurement method characterized by measuring an SDI value of a separation membrane supply liquid using a membrane filter having a contact angle (θ) of 70 ° or less.

  In the process of passing membrane filtrate for 15 minutes when the SDI measurement is performed using membrane filtrate pretreated with MF or UF as the reason why the SDI value indicates an abnormal value as described above. Fine particles and microbubbles that are present in the membrane filtration water and are much smaller than the membrane filter with a pore size of 0.45 μm are adsorbed on the wall surface of the polymer microchannel structure that constitutes the filter, and the pore channel area It was inferred that this was caused by narrowing the pores or partially blocking the pore flow paths. It was inferred that microbubbles were particularly influential. In the present invention, an SDI measurement method has been found in which the influence of microbubbles can be reduced by using a membrane filter having a contact angle (θ) of 70 ° or less, and a highly accurate SDI value can always be calculated. It is. Further, in order to calculate a highly accurate SDI value, the contact angle (θ) is preferably 65 ° or less.

  Here, the contact angle (θ) refers to an angle formed by a tangent line drawn at the contact point between the solid surface and the liquid droplet and the solid surface. In the present invention, the contact angle was measured by a liquid method in which one drop of 0.1 μl of distilled water (pure water) was obtained from the shape of the drop when placed on the smooth surface of the membrane filter. Detailed measurement methods are as described in the examples.

  The membrane filter preferably contains a fluorine-containing polymer as a forming material. By using a fluorine-containing polymer as a forming material, a membrane filter having long-term stability can be obtained.

  The present invention also relates to an SDI measuring device including at least a membrane filter having a contact angle (θ) of 70 ° or less.

  The membrane filter preferably contains a fluorine-containing polymer as a forming material. By using a fluorine-containing polymer as a forming material, a membrane filter having long-term stability can be obtained.

  Furthermore, the present invention relates to a fresh water generation method using a reverse osmosis membrane including a step of measuring an SDI value by the above method for a part of a separation membrane feed solution.

  By using the SDI measurement method of the present invention, a highly accurate SDI value can always be calculated. Thereby, the contamination risk of the separation membrane such as the reverse osmosis membrane can be predicted in advance and accurately, and the subsequent membrane process can be efficiently and stably operated.

  The SDI measurement method of the present invention uses a membrane filter with a contact angle (θ) of 70 ° or less, and can measure the measurement device, pressure control method, separation membrane feed water type, temperature, The pH and the like are not particularly limited.

  Hereinafter, a specific example of the SDI measuring method of the present invention will be described with reference to FIGS. FIG. 1 shows a configuration example of an SDI measuring apparatus 1 used in the SDI measuring method of the present invention. In FIG. 1, an SDI measuring apparatus 1 includes a filter holder 2 as a membrane separation means, a holder main valve 3, a pressure adjustment valve 4 as a pressure adjustment means, a sample tank 5, a tank original valve 6, a pressure reducing valve 7, and a pressurizing means. And a measuring cylinder 9 for measuring the amount of filtrate. The filter holder 2 is equipped with a membrane filter having a hole diameter of 0.45 μm and a diameter of 47 mm as defined in ASTM.

  The material for forming the membrane filter is not particularly limited as long as the contact angle (θ) is 70 ° or less. Examples of the forming material include polymer materials such as cellulose mixed polyester, polyvinylidene fluoride, polytetrafluoroethylene, polycarbonate, and polyethersulfone. In particular, from the viewpoint of long-term stability of the membrane filter, it is preferable to use a fluorine-containing polymer such as polyvinylidene fluoride or polytetrafluoroethylene. Examples of the membrane filter include Durapore Membrane Filter model HVLP04700 (pore diameter 0.45 μm, filter diameter φ47 mm) manufactured by Millipore.

  When the contact angle (θ) of the membrane filter exceeds 70 °, the accuracy of the SDI value is lowered and the accurate value is not shown.

  The sample tank 5 stores sand filtration or membrane filtration water such as seawater and sewage pretreated by MF, UF, or DMF (two-layer filter made of sand-anthracite). The pretreatment method using MF, UF or the like is not particularly limited, and can be performed by a commonly used method.

  As an SDI measurement method, first, the pressure inside the sample tank 5 is increased so that the pressure becomes higher than the pressure prescribed by ASTM by adjusting the pressure reducing valve 7 and the tank main valve 6 provided in the gas cylinder 8. Then, sand filtration or membrane filtration water is introduced into the pressure control valve 4, and the pressure control valve 4 is adjusted to reduce the pressure to a pressure (206 kPa) defined in ASTM. Then, the said sand filtration or membrane filtration water is introduce | transduced into the filter holder 2, and SDI measurement is performed on the said conditions prescribed | regulated to ASTM. ASTM does not specify the measurement temperature, but in order to measure an accurate SDI value, it is preferable to keep the temperature constant during the measurement. Usually, measurement temperature is about 5-35 degreeC. If the measurement temperature is 40 ° C. or higher, the RO performance tends to be abnormal, so measurement with pretreated water at the temperature or higher is not preferable. Moreover, although the pH of the sample used for the measurement is not defined in ASTM, it is preferable to adjust the pH to about 6.5 to 7 in advance in order to prevent generation of scale in the reverse osmosis membrane treatment.

  FIG. 2 shows another example of the SDI measuring apparatus 1 used in the SDI measuring method of the present invention. The measurement conditions are the same as described above. In FIG. 2, the SDI measuring apparatus 1 includes a high-pressure pump 10 instead of the gas cylinder 8. In the SDI measurement method using the SDI measurement device 1, first, filtered water in the sample tank is sucked from the high-pressure pump inlet, and the high-pressure pump applies high pressure to the filtered water so that the pressure is higher than the pressure specified by ASTM. Discharge from the pump outlet. Then, after the pressure is reduced by the pressure reducing valve 7, the pressure is reduced to a pressure (206 kPa) regulated by ASTM by adjusting the pressure regulating valve 4 to the pressure regulating valve 4 provided with a pipe branched for regulating the flow rate. Thereafter, filtered water is introduced into the filter holder 2 and SDI measurement is performed under the conditions specified in ASTM. The branched pipe is provided for adjusting the discharge flow rate from the branch pipe in order to prevent the set pressure from increasing due to the decrease in the permeation flux of the membrane filter.

  The SDI value measured by the above method does not show an abnormal value even when seawater or sewage after pretreatment in which micro bubbles are present is measured, and can always be calculated accurately. Therefore, if the SDI measurement process according to the above method is incorporated in seawater and sewage production processes using reverse osmosis membranes, it is very effective as a monitoring index for reverse osmosis membrane supply water, and the reverse osmosis membrane process can be operated stably. Is possible.

  The reverse osmosis membrane process uses a reverse osmosis membrane having the property of selectively permeating water molecules, and applies a pressure higher than the osmotic pressure of the solution to the solution and water in osmotic equilibrium across the reverse osmosis membrane. This is a technique for transferring water molecules in the solution to the water side by adding from the above. In other words, the reverse osmosis membrane process can extract water from the solution without causing a phase change as in the evaporation method, and is therefore energy efficient and easy to manage.

  And when performing this reverse osmosis membrane separation on a practical scale, the following reverse osmosis separation devices are usually used. First, a reverse osmosis membrane is processed into a spiral, tubular, flat membrane laminate, or hollow fiber membrane shape, and is housed in a case with a flow channel material interposed therebetween to form a membrane element called an element. These elements are appropriately connected in series and housed in a pressure vessel to form a module. Further, the modules are connected in parallel to form a reverse osmosis separation module unit. Then, reverse osmosis separation is performed by applying a predetermined pressure to the entire reverse osmosis separation module unit.

  Hereinafter, the specific example of the fresh water generation method using a reverse osmosis membrane is demonstrated based on FIG. In FIG. 3, the reverse osmosis separation device 12 includes a reverse osmosis membrane module unit 16, a high-pressure pump 10, and the like. The raw seawater 13 is pretreated by a turbidity removal device 14 (device equipped with MF, UF, DMF, or the like) to become reverse osmosis supply water 15, and this supply water 15 is adjusted to a predetermined operating pressure by the high-pressure pump 10. The pressure is increased until it is introduced into the reverse osmosis membrane module unit 16, where it is separated into permeated water 17 a that has been subjected to reverse osmosis treatment to remove salts and the like and concentrated water 17 b that has been concentrated with salts and the like. In the case of this reverse osmosis separation device 12, reverse osmosis separation is performed in one stage at a single operating pressure, but multistage reverse osmosis separation may be performed. The permeated water 17a thus obtained is appropriately stored in the tank 18 and used as demineralized water.

  In the present invention, the reverse osmosis feed water as a sample is extracted at any location before the reverse osmosis separation module unit 16 is introduced into the reverse osmosis separation module unit 16, and the SDI measurement is performed by the method described above. Since the operation pressure by the high-pressure pump 10 is generally 3 MPa or more for seawater desalination, the SDI measurement is performed after the pressure is reduced to the pressure (206 kPa) defined in ASTM. Then, the degree of contamination of the supplied water can be confirmed from the calculated SDI value, and the subsequent operation can be performed while appropriately changing the operating conditions.

Examples and the like specifically showing the configuration and effects of the present invention will be described below. The SDI ₁₅ value was measured under the conditions specified in ASTM and calculated by the following formula.

SDI ₁₅ = (1-T ₀ / T ₁₅ ) × 100/15
T ₀ : Time (seconds) required to filter a sample at a pressure of 206 kPa through a membrane filter having a pore diameter of 0.45 μm and a diameter of 47 mm and filter an initial sample of 500 ml
T ₁₅ : The time (seconds) required for further filtering for 15 minutes and then filtering 500 ml of the sample
(Measurement method of contact angle)
The contact angle (θ) was measured by using a contact angle measuring device (Kyowa Interface Science Co., Ltd., CA-X type), and 1 drop of 0.1 μl distilled water (pure water) was placed on the smooth surface of the membrane filter. It was measured by a liquid suitability method for obtaining the angle from the shape of the droplet. The measurement conditions are such that the droplet temperature is 15 ° C., the filter surface temperature is 17 ° C., and the influence of weight is negligible in the horizontal state.

Example 1
SDI measurement was performed using the SDI measuring apparatus having the configuration shown in FIG. The membrane filter used (Millipore, Durapore Membrane Filter HVLP04700) was made of polyvinylidene fluoride as a raw material, and the contact angle was 65 °. As a measurement sample, seawater near the Gulf of Arabia and Bahrain was used, and filtered water pretreated with a UF membrane (manufactured by Nitto Denko Corporation, RS50-S8) was used. Pretreated filtered water (pH: about 8.2) is stored in a sample tank, discharged using a high pressure pump (manufactured by Hydra-cell, F20-X) with pressure applied to the filtered water, and a pressure control valve The pressure was reduced to 206 kPa, filtered water was introduced into a filter holder equipped with the membrane filter, and SDI measurement was performed under the conditions specified in ASTM. The measurement temperature was about 17 ° C. The relationship between the SDI ₁₅ value and the processing time is shown in FIG. As can be seen from FIG. 4, the use of a membrane filter with a contact angle of 65 ° makes it possible to always calculate a highly accurate SDI value, and the SDI value variation is extremely small.

Example 2
SDI measurement in the same manner as in Example 1 except that a membrane filter made of polytetrafluoroethylene (Millipore, Fluoropore Membrane Filter JHWP04700, contact angle 56 °) was used instead of the membrane filter described in Example 1. Went. The relationship between the SDI ₁₅ value and the processing time is shown in FIG. As is apparent from FIG. 4, it can be seen that by using a membrane filter having a contact angle of 56 °, a highly accurate SDI value can always be calculated, and variation in the SDI value is small.

Comparative Example 1
Instead of the membrane filter described in Example 1, a membrane filter using cellulose mixed polyester as a raw material (manufactured by Millipore, MF-Millipore Membrane Filter HAWP04700, contact angle 88 °) was used in the same manner as in Example 1, but SDI was used. Measurements were made. The relationship between the SDI ₁₅ value and the processing time is shown in FIG. As can be seen from FIG. 4, when a membrane filter having a contact angle of 88 ° is used, the accuracy of the SDI value is low and the variation in the SDI value is extremely large.

Example 3
SDI measurement was performed using the SDI measuring apparatus having the configuration shown in FIG. The membrane filter used is the same as in Example 1. As a measurement sample, seawater near the Gulf of Arabia Bahrain was used, and filtered water pretreated with a UF membrane (manufactured by Nitto Denko Corporation, RS50-S8) was used. Then, only the surface of the membrane filter on the filtered water introduction side was immersed in the filtered water for a certain time, and then SDI measurement was performed in the same manner as in Example 1. The pH of the filtered water was about 8.2, and the measurement temperature was about 31 ° C. The relationship between the SDI ₁₅ value and the immersion time is shown in FIG. As is apparent from FIG. 5, it can be seen that by using a membrane filter with a contact angle of 65 °, a highly accurate SDI value can always be calculated, and variation in the SDI value is small. That is, it is considered that the membrane filter having a contact angle of 65 ° is hardly affected by microbubbles in the filtered water.

Comparative Example 2
SDI measurement was performed in the same manner as in Example 3 except that the membrane filter described in Comparative Example 1 was used instead of the membrane filter described in Example 3. The relationship between the SDI ₁₅ value and the immersion time is shown in FIG. As can be seen from FIG. 5, when a membrane filter having a contact angle of 88 ° is used, the accuracy of the SDI value is low and the variation in the SDI value is large. That is, it is considered that the membrane filter having a contact angle of 88 ° is easily affected by microbubbles in the filtered water.

It is a figure which shows the structural example of an SDI measuring apparatus. It is a figure which shows the other structural example of an SDI measuring apparatus. It is a figure which shows the flow of the fresh water generation method using a reverse osmosis membrane. It is a diagram showing a relationship between SDI ₁₅ value and processing time. It is a diagram showing a relationship between SDI ₁₅ value and the immersion time.

Explanation of symbols

1: SDI measuring device 2: Filter holder 3: Holder valve 4: Pressure control valve 5: Sample tank 6: Tank valve 7: Pressure reducing valve 8: Gas cylinder 9: Measuring cylinder 10: High pressure pump 11: Pressure gauge 12: Reverse Osmosis separation device 13: Raw seawater 14: Turbidity removal device 15: Reverse osmosis feed water 16: Reverse osmosis membrane module unit 17a: Permeate water 17b: Concentrated water 18: Tank

Claims (5)

An SDI measurement method, wherein an SDI value of a separation membrane supply liquid is measured using a membrane filter having a contact angle (θ) of 70 ° or less. The SDI measurement method according to claim 1, wherein the membrane filter contains a fluorine-containing polymer as a forming material. An SDI measuring apparatus having at least a membrane filter having a contact angle (θ) of 70 ° or less. The SDI measuring apparatus according to claim 3, wherein the membrane filter contains a fluorine-containing polymer as a forming material. A fresh water generation method using a reverse osmosis membrane comprising a step of measuring an SDI value by a method according to claim 1 or 2 for a part of a separation membrane feed solution.

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